Systems and methods for accurately measuring fluid

ABSTRACT

The present invention relates to systems and methods for measuring the amount of fluid. A fluid source is in fluid communication with a measuring system. The fluid source includes a non-collapsible walled container for dispensing or introducing fluid. The measuring system includes a sensor in fluid communication with the container that senses the volume of the gas, and a system that calculates the amount of fluid flowing through an opening of the container based on the amount of gas flowing through an opening of the container. The volume of gas entering or exiting the container is measured rather than directly measuring the amount of fluid leaving or entering the container to determine in a more accurate, less complicated and less expensive manner the volume of fluid.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/785,656, filed Feb. 16, 2001 now abandoned, entitled “SYSTEMS ANDMETHODS FOR ACCURATELY MEASURING FLUID,” which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to systems and methods for accuratelymeasuring an amount of fluid. More specifically, the present inventionis directed to systems and methods for using a measurement of the amountof gas to measure, in a sterile, reliable and accurate manner, theamount of fluid that is dispensed from or introduced into a container.

2. Background and Related Art

Since the beginning of science, practitioners have been required tomeasure the amount of liquid transferred from one container to anothercontainer or location. Traditional methods for performing such liquidtransfer measurements have included the use of such devices as measuringcups or liquid flow meters. While each method has its own distinct andunique advantage, a number of drawbacks exist in the utilization of thetraditional methods for measuring liquid transferred or dispensed from acontainer. As an example, the traditional methods can expose thetransferred liquid to impurities within the environment, such asair-born bacteria, and allow for the introduction of human error intothe measurements. The methods can also be complex and expensive, andunable to accurately measure low volumes of liquids due to varyingdensities and viscosities.

Additional drawbacks are specific to the application for which theliquid transfer measurements are being performed. By way of example, onearea where practitioners are required to accurately measure the amountof liquid transferred or dispensed from a container is in the medicalarea of radiology, in which a radiopaque liquid known as “contrastmedium” is inserted into a patient's body so as to provide a contrast indensity between the area of the body that is being x-rayed and thecontrast medium inserted.

When fluid, such as contrast medium, is intravenously administered, itis critical that air bubbles are not inadvertently introduced into thepatient's vascular system. It is, therefore, important that thepractitioner monitor and continually assess the amount of mediumremaining in the container in order to prevent any possibility ofinadvertently injecting air bubbles into the patient. Administering anexcess amount of fluid, such as contrast medium, can also injure apatient. Due to the current expense of contrast medium, it is also veryimportant for the practitioner dispensing the contrast medium to performthe process in a manner that results in the least amount of waste. Foraccurate billing and cost assessment purposes, a practitioner isrequired to monitor the exact amount of contrast medium that isdelivered to each patient over the course of the patient's medicalprocedure or hospital stay. However, monitoring the exact amount ofcontrast medium administered to a patient is difficult, particularlywhen multiple contrast medium dispensers are used or when a dispenser isshared between two patients. This inability to accurately monitor theexact amount of medium administered can result in patients beingincorrectly charged. The inaccuracies complicate any determination as tothe amount of useful medium remaining in a dispenser and often result inthe remainder being discarded rather than being used on a new patient.Given the high cost, such waste of contrast medium can translate intosignificant financial losses for facilities that perform a large numberof these fluid-dispensing procedures.

This need to accurately measure the amount of contrast medium dispensedis one example of the current need to accurately and reliably measureliquid that is dispensed from a container.

SUMMARY OF THE INVENTION

The present invention is directed to systems and methods for using ameasurement of the amount of gas entering or exiting a container tomeasure, in a sterile, reliable and accurate manner, the amount of fluidthat is dispensed from or introduced into a container.

Implementation of the present invention is performed in association witha non-collapsible container. The container comprises a rigid materialsuch that as fluid is dispensed from the container and a vacuum iscreated, the container walls do not collapse. A measuring system thatincludes a sensor is in fluid communication with the container.

In one implementation of the present invention, a sensor is used forsensing the volume of the gas entering or exiting the container. Thesensor can be a single sensor that performs both functions of sensingboth the mass flow and the density of the gas, or can be a dual sensorwherein one sensor component senses the mass flow and another sensorcomponent senses the density. Optionally, a measurement of the gasdensity can be preprogrammed into the sensor or calculating system suchthat the sensor only senses gas flow. The volume of gas entering orexiting the container may also be measured in a variety of differentmanners.

The calculating system calculates the amount of fluid dispensed from orintroduced into the container based on the amount of gas flowing into orout of the container. The calculating system typically comprises anelectrical system that includes a microprocessor and/or ananalog-to-digital converter, but can comprise a variety of differentsystems, such as a mechanical system that determines the amount of gasflowing due to fluid dispensed from or introduced into a container. Thefluid may comprise a liquid, such as contrast medium or a variety ofdifferent fluids.

A filtering system may optionally be used to maintain a sterileenvironment and to protect the sensor. Therefore, in light of theoverall system, the gas entering or exiting the container is measuredrather than directly measuring the amount of fluid leaving or enteringthe container, causing the measurement to be more accurate, lesscomplicated, and less expensive.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be obvious from thedescription, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 illustrates a syringe in fluid communication with a fluid sourcethat dispenses fluid to the syringe and is in fluid communication with acalculating system that calculates the volume of fluid dispensed; and

FIG. 2 is a flow chart that illustrates an exemplary embodiment forcalculating the volume of fluid dispensed from a container based on massflow and density measurements of gas that enters the container due tothe fluid being dispensed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention extends to systems and methods for measuring theamount of fluid. More specifically, the present invention is directed tosystems and methods for using a measurement of a volume of gas tomeasure, in a sterile, reliable and accurate manner, the volume of fluidthat is dispensed from or introduced into a container. The embodimentsof the present invention may comprise a fluid source coupled in fluidcommunication to a calculating system, as will be discussed in greaterdetail below.

Throughout the disclosure, reference is made to calculating the volumeof fluid based on the amount of gas that flows through an opening of acontainer as a result of fluid flowing through an opening of acontainer. In the disclosure and in the claims the term “gas” refers toany type of gas or combination of gasses that are allowed to enter thefluid source. As such, the term “gas” may refer to hydrogen, helium,nitrogen, oxygen, or any other gas or a combination of gases, includingair, for example. Furthermore, in the disclosure and in the claims, theterm “opening” may refer to any aperture or channel, including a portcoupled to or integral with the container, for example, through whichgas and/or fluid can flow.

Embodiments of the present invention comprise a gas source, a fluidsource and a measuring system. In one embodiment, the gas sourceincludes a tank or container having a gas therein. In anotherembodiment, the gas source is the surrounding atmospheric environmentand the gas contained therein is the atmospheric air.

The fluid source includes a non-collapsible walled container havingfluid therein. The gas source is coupled in fluid communication with thefluid source so as to allow gas from the gas source to enter or exit thefluid source as fluid flows. In one embodiment, the measuring system isinterposed between the gas and fluid sources and measures the mass flowand density of the gas that is transferred between the gas source andthe fluid source so as to calculate the amount of fluid dispensed fromthe fluid source based on the volume of gas flowing into the fluidsource. As such, in accordance with the present invention, the amount offluid dispensed is measured in a more accurate, less complicated, andless expensive manner.

With reference now to FIG. 1, an example of a suitable environment inwhich the invention may be implemented is provided. While the embodimentof FIG. 1 illustrates a fluid dispensing system 100 that may be used inconnection with a fluid delivery system 140, those skilled in the artwill appreciate that the present invention may be practiced in a varietyof system configurations that include a fluid source, a gas source, andsome kind of a measuring system so as to measure the amount of fluiddispensed.

In FIG. 1, an exemplary system for implementing the present invention isillustrated as fluid dispensing system 100, which includes a measuringsystem 120 interposed between a gas source 110 and a fluid source 130.As fluid is dispensed or displaced from fluid source 130, gas flows fromgas source 110, through measuring system 120, and into fluid source 130,as will be further explained below.

Gas source 110, may be any type of gas supply that contains gas therein,including a tank, a container and/or the atmospheric environment. In anembodiment where gas source 110 is an enclosed tank or container havinggas stored therein, gas source 110 is coupled in fluid communicationwith measuring system 120. In an alternative embodiment, where gassource 110 is the atmospheric environment surrounding the fluiddispensing system 100, a gas inlet port coupled to the measuring system120 allows air to enter into the measuring system 120.

Measuring system 120 senses the volume of gas entering a container ofthe fluid source as fluid is dispensed therefrom and thereby calculatesthe volume of fluid dispensed. In the embodiment of FIG. 1, measuringsystem 120 comprises a sensor for sensing the mass flow and density ofthe gas entering a container 132 of the fluid source 130. The sensor ofthe present invention can be a single sensor that performs bothfunctions of sensing the mass flow of gas and the density of gas, or canbe a dual sensor wherein one sensor component senses the mass flow ofgas and another sensor component senses the density of gas. Optionally,a measurement of the gas density can be preprogrammed into the sensor orthe calculating system such that the sensor only senses the mass flow ofthe gas, as will be further explained below. Optionally, the volume ofgas entering the container may be measured in a variety of differentmanners.

In FIG. 1, the sensor is a dual sensor wherein one sensor component isillustrated as sensor 122, which is in fluid communication with an inletport 121 a and an outlet port 121 b, and another sensor component isillustrated as density sensor 123. Sensor 123 measures the density ofthe air or other gas. Gas from gas source 110 (e.g., air) enters inletport 121 a, flows through sensor 122, and exits outlet port 121 b. Asthe gas flows through sensor 122, the mass flow of the gas is measured.Sensor 122 is an example of a means for sensing the amount of gasflowing. While sensor 122 may be any sensor that measures the mass flowof gas, in the illustrated embodiment sensor 122 is a mass flow meter.By way of example, one mass flow meter that may be used as sensor 122 isan AWM3000 series mass airflow sensor that is available from HoneywellInc., 11 West Spring Street; Freeport, Ill. 61032. Sensor 123 maycomprise a barometer or altimeter, for example.

As illustrated in FIG. 1, measuring system 120 may further comprise acalculating system 124 that is in communication with sensor 122.Calculating system 124 is an example of a means for calculating theamount of fluid displaced and may comprise one or more mechanical and/orelectrical systems that are used to calculate the amount of gas thatenters fluid source 130 based on a measurement of the mass flow of gasthrough sensor 122 and a measurement of the density of the gas. In theillustrated embodiment, the measurement for the mass flow of gas isobtained by sensor 122 and the measurement for the density of gas isobtained by density sensor 123. Both the measurement of the mass flow ofgas and the density of gas are transmitted to calculating system 124.Optionally, calculating system 124 is preprogrammed with a measurementof the density of the gas. Sensor 123 and a preprogrammed calculatingsystem 124 are each examples of means for obtaining a density value of agas.

An electrical system of calculating system 124 may comprise ananalog-to-digital converter and/or a special purpose or general purposecomputer including various computer hardware and/or software forcalculating the amount of gas flowing into a fluid source. Calculatingsystem 124 may further include a computer-readable medium for carryingor having computer-executable instructions or data structures storedthereon that can be accessed by a general purpose or special purposecomputer. Computer-executable instructions comprise, for example,instructions and/or data structures that cause a general purposecomputer, special purpose computer, or special purpose processing deviceto perform a certain function or group of functions, such as calculatingthe amount of gas flowing into a fluid source.

Those skilled in the art will appreciate that calculating system 124 maycomprise computing environments with many types of computer systemconfigurations, such as a personal computer, calculator, hand-helddevice, multi-processor system, microprocessor-based or programmableconsumer electronic device, a network PC, minicomputer, mainframecomputer, or one or more similar devices, for example. In oneembodiment, calculating system 124 comprises a general purpose computingdevice in the form of a conventional computer that is coupled to anoutput device 126, such as a monitor, printer, speaker or other outputdevice. Output device 126 is an example of a means for informing a userof the amount of fluid displaced and may include a visual and/or audiblenotification to inform a user as to the amount of fluid displaced oralternatively the amount of fluid available for displacement.Furthermore, calculating system 124 may operate in a networkedenvironment using logical connections to one or more remote computers.

Fluid source 130 is coupled in fluid communication to measuring system120 and includes a container 132 having fluid therein. Container 132 isan example of a non-collapsible means for containing fluid. In theillustrated embodiment, container 132 is a non-collapsible walledcontainer that comprises a rigid material. Examples of such rigidmaterials include glass, plastic, metal, wood, or any other materialthat is non-deformable such that as the fluid is dispensed from thecontainer and a vacuum is created, the container walls do not collapse.

Coupled to container 132 are one or more ports. The ports allow forfluid to be dispensed or displaced from container 132 and gas to enterinto container 132. In the illustrated embodiment, a vented spike 134 iscoupled to container 132 to provide the one or more ports. The ventedspike 134 includes a gas inlet port 136 and a fluid outlet port 138,each of which is configured to be placed in fluid communication with acontainer connection port 137 configured to be in fluid communicationwith container 132. Gas inlet port 136 is configured to be in fluidcommunication with sensor 122, port 138 is configured to be in fluidcommunication with fluid delivery system 140, and port 137 is configuredto be in fluid communication with container 132.

By way of example, a type of vented spike that may be used as spike 134to allow liquid to dispense from container 132 and gas to entercontainer 132 is a Burron OEM vented piercing device, aka a dual flowpiercing device, available from Burron OEM, a division of B. BraunMedical, Inc., 824 12^(th) Avenue, Bethlem, Pa. 18018.

Spike 134 allows gas to enter container 132 through port 137 while fluidexits container 132 and flows into fluid delivery system 140 throughport 138. Nevertheless, while FIG. 1 illustrates a vented spike having afluid outlet port, a container port and a gas inlet port, a variety ofone or more ports may be employed to allow the fluid to dispense fromcontainer 132 and gas to enter into container 132. By way of example,one port may be employed for both the inflow of gas and outflow offluid. Alternatively, a plurality of ports may be utilized, includingone or more gas inlet ports coupled in fluid communication to container132 and one or more fluid outlet ports coupled in fluid communication tocontainer 132. A plurality of gas inlet ports and/or a plurality offluid outlet ports may be utilized, or any other combination of one ormore ports to allow fluid to dispense from container 132 and gas toenter into container 132. By way of example, the fluid container maycomprise a vented bottle having a non-vented spike coupled thereto.

As fluid is dispensed from fluid source 130, gas is transferred from gassource 110, through measuring system 120 and into fluid source 130. Thetransfer of the gas occurs from a hydrostatic pressure in the fluidsource 130 that causes the gas to flow from gas source 110, and intofluid source 130. As the gas flows through the measuring system 120, theflow and density of the gas flowing therethrough is obtained tocalculate the amount of fluid dispensed based on the amount of gasflowing into the fluid source 130.

To provide for and maintain a sterile environment, fluid dispensingsystem 100 may optionally include a filtering system coupled to sensor122 in order to eliminate any impurities present in the gas. In theillustrated embodiment, the filtering system comprises filters 128 a,128 b and 133, where filter 128 a is coupled at inlet port 121 a, filter128 b is coupled to outlet port 121 b, and filter 133 is coupled to gasinlet port 136 of fluid source 130. While the filtering systemillustrated in FIG. 1 includes three filters, embodiments of the presentinvention include filtering systems having more than three filters orless than three filters.

When fluid is dispensed from the fluid source 130, hydrostatic pressurein fluid source 130 causes gas to be transferred from the gas source110, through the measuring system 120 and into the fluid source 130. Asthe gas flows through the measuring system 120, an amount of gas flowingtherethrough is measured to calculate the volume of fluid dispensedbased on the volume of gas flowing into the fluid source 130.

While the embodiment of FIG. 1 illustrates a fluid dispensing system,embodiments of the present invention also embrace systems and methodsfor calculating a volume of fluid introduced into a container. In suchembodiments, the measuring system calculates the volume of fluidintroduced by sensing the flow of air exiting the container as fluid isintroduced. Furthermore, embodiments of the present invention alsoembrace systems and methods for calculating the volume of fluiddispensed and introduced by sensing air flow. By way of example, abi-directional sensor may be employed to sense the flow of air into orout of the container due to the respective flow of fluid out of or intothe container. Such systems are particularly useful when the fluid is,for example, an expensive fluid and any portion of the fluid that isdispensed from the container but has remained unused (i.e. remained inthe sterile environment) can be saved by being introduced back into thecontainer. As such, a total volume of fluid can be obtained even afterfluid is dispensed and then re-introduced into the container. Therefore,the systems and methods of the present invention accurately calculate anamount of fluid dispensed and/or introduced.

In one embodiment, the calculating system calculates the amount of fluiddispensed as depicted and discussed with reference to the flow chart ofFIG. 2. In one embodiment, the gas source 110 is the atmospheric air anddensity sensor 123 measures the density of the atmospheric air whilesensor 122 measures the mass flow of the air flowing therethrough.

In FIG. 2, execution begins at decision block 150 where a determinationis made as to whether or not the components of the measuring system havebeen zeroed. The process of zeroing (e.g., initializing) components thatare used to obtain measurements can provide a more accurate measurement,and is more fully described in U.S. Pat. No. 5,807,321, entitled SYSTEMFOR ELECTRONICALLY MONITORING THE DELIVERY OF CONTRAST MEDIA, filed Sep.15, 1998, which is incorporated herein by reference. If it is determinedat decision block 150 that the components of the measuring system havebeen zeroed, execution proceeds to decision block 154. Alternatively, ifit is determined that the components of the measuring system have notbeen zeroed, execution proceeds to step 152 for the automatic zeroing ofthe components of the measuring system and execution then proceeds todecision block 154.

At decision block 154, a determination is made as to whether or not thedensity of gas has been measured or provided. By way of example, theunits of the density of gas are mass per volume (e.g., g/cc). Asprovided above, the density of gas may be measured by the same sensorcomponent that measures the mass flow of gas or by a separate densitysensor component. If it is determined at decision block 154 that thedensity of gas has been measured, execution proceeds to step 158.Alternatively, if the density of gas has not been measured, executionproceeds to step 156, where a value is obtained for the density of thegas and then execution proceeds to step 158.

At step 158, dispensing of the fluid contained within thenon-collapsible walled container begins. The dispensing of the fluidcauses a hydrostatic pressure within the non-collapsible walledcontainer to change, resulting in gas flowing from the gas source,through the measuring system and into the non-collapsible walledcontainer of the fluid source. As the gas flows, the mass flow of gas ismeasured by a sensor at step 160 and is communicated to the calculatingsystem. The units of the mass flow of gas are, for example, grams persecond (g/s). At step 162, the mass flow of gas measurements obtained atstep 160 are received by the calculating system, which calculates theamount of fluid dispensed from the non-collapsible walled container ofthe fluid source based on the mass flow and the density of the gas.

At step 164, the calculating system eliminates any gas density offsetfrom the measurements obtained at step 160 of the mass flow of gas. Forexample, dividing the mass flow (e.g., g/s) by the density (e.g., g/cc)to yield flow (e.g., cc/s) eliminates the density offset. At times, thevolume flow of fluid (e.g., cc/s) is what is desired to be output on anoutput system. In such instances, the flow of gas (e.g., cc/s) obtainedat step 164 corresponds to the volume flow of fluid (e.g., cc/s) and isthus output on an output system at step 168. By way of example, volumeflow can be calculated as depicted in Equation 1 below. $\begin{matrix}{\text{Volume~~Flow} = {\frac{massflow}{density} = {\frac{\frac{g}{s}}{\frac{g}{cc}} = \frac{cc}{s}}}} & \text{Equation~~1}\end{matrix}$

Alternatively, it may be desired to obtain the total volume of fluid.Therefore, once the flow of gas (e.g., cc/s) is obtained at step 164,execution proceeds to step 166 to calculate the total volume of gas(e.g., cc), which corresponds to the total volume of fluid.

At step 166, the volume of the gas that entered into the non-collapsiblewalled container is calculated. While the volume of gas can becalculated in a variety of manners, one way of calculating the volume isillustrated by the present example and includes obtaining the parametersof mass flow (step 160) and density of the gas (step 156), eliminating adensity offset (step 164), and at step 166 integrating with respect totime the gas flow obtained at step 164. The volume of the gas thatentered into the non-collapsible walled container represents the volumeof fluid dispensed therefrom. By way of example, the total volume may becalculated as depicted in Equation 2 below. $\begin{matrix}{\text{Total~~Volume} = {{\int{\text{Volume~~Flow} \cdot {t}}} = {{\int{\frac{cc}{s} \cdot {t}}} = {cc}}}} & \text{Equation~~2}\end{matrix}$

Execution then proceeds to step 168 for outputting (e.g., displaying,broadcasting, transmitting, etc.) the total volume of fluid dispensed ona display screen, digital display, or other output system. The volume offluid dispensed may be displayed in a variety of manners, includinggraphically, by percentage, pictorially, or otherwise. Furthermore, thedisplay screen or other output system may display the volume of fluiddispensed from the fluid source, the volume of fluid currently availablein the fluid source, the volume delivered to a particular patient, etc.

Thus, the present invention extends to both systems and methods formeasuring the amount of fluid dispensed from and/or introduced into afluid source through the utilization of the flow and density of gas. Thepresent invention may measure liquid such as a contrast medium, or otherliquids, gasses, or fluids. A practitioner or user can therefore know atany given instant in time the amount of liquid (such as a contrastmedium or other fluid) that has been dispensed from a fluid source andthe amount of fluid still available in the fluid source. Furthermore,the systems and methods of the present invention measure and obtain theamount of fluid in a sterile, reliable and accurate manner.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A system configured for containing a fluid and for sensingan amount of fluid that flows through the system, the system comprising:a non-collapsible container configured to hold a fluid, the containerincluding a opening through which the fluid can flow, and the fluidcomprising a contrast medium; a sensor that is disposed outside of thecontainer and that is in fluid communication with the container, thesensor being configured to measure an amount of a gas that flows throughthe sensor in direct response to hydrostatic pressure that is created bythe flow of the fluid through the container, the gas comprisingatmospheric air; a calculating system configured to calculate an amountof the fluid that flows through the container based upon the amount ofgas that flows through the sensor.
 2. A system as recited in claim 1,wherein the sensor senses a mass flow of gas and a density value of gasflowing through the sensor.
 3. A system as recited in claim 1, furtherincluding a filter system coupled in fluid communication to said firstsensor component, the filter system being configured to removeimpurities from the gas.
 4. A system as recited in claim 1, wherein thecalculating system includes at least one of an analog-to-digitalconverter and a processor.
 5. A system as recited in claim 1, whereinthe calculating system is configured to calculate a volume of fluiddispensed from the container, a volume of fluid introduced into thecontainer, and a volume of fluid currently available in the container.6. A system as recited in claim 1, further including a display devicethat is configured to display at least one of a volume of fluiddispensed from the container, a volume of fluid introduced into thecontainer, a volume of fluid currently available in the container, and avolume of fluid delivered to a particular patient.
 7. A system asrecited in claim 1, wherein the fluid is a sterile fluid.
 8. A system asrecited in claim 1, further including a filter for filtering impuritiesfrom the gas.
 9. A system as recited in claim 1, further including adensity sensor for identifying a density values of the gas.
 10. A systemas recited in claim 2, wherein the calculating system calculates anamount of the fluid that flows through the opening in the containerbased upon the mass flow and the density value.
 11. A system as recitedin claim 2, wherein the sensor is a dual sensor comprising: a firstsensor component for sensing the mass flow; and a second sensorcomponent for sensing the density value.
 12. A method for measuring anamount of fluid flowing through a system that includes a non-collapsiblecontainer, a sensor and a calculating system, wherein the sensor isexternally located from the container and in fluid communication withthe container, such that a flow of a fluid through the container createshydrostatic pressure at the sensor, the method comprising: causing afluid to flow through an opening in the container, thereby creatinghydrostatic pressure between the container and the externally locatedsensor, and such that a gas is caused to flow through the sensor inresponse to the hydrostatic pressure; measuring the amount of gasflowing through the sensor in response to the hydrostatic pressure,including: measuring a mass flow of the gas at the sensor, andidentifying a density value of the gas by including at least one ofmeasuring the density value with a density sensor and receiving userinput at the system comprising a predetermined density value;calculating an amount of fluid that has flowed through the opening inthe container based at least in part on the measured amount of gasflowing through the sensor wherein the method of calculating the amountof fluid includes: dividing the mass flow of the gas by the densityvalue of the gas to obtain a volume flow of the gas; and integrating,with respect to time, the mass flow of the gas to calculate the volumeof gas that has flowed through the opening in the container, wherein thevolume of gas corresponds directly to a volume of fluid that has flowedthrough the opening in the container.
 13. A method as recited in claim12, wherein causing a fluid to flow through an opening in the containercomprises one of dispensing the fluid from the container and introducingthe fluid into the container.
 14. A method as recited in claim 12,further including: filtering impurities from the gas flowing through thesensor.
 15. A method as recited in claim 12, wherein the gas flows intothe container as it flows through the sensor.
 16. A method as recited inclaim 12, wherein the calculating system is connected with an outputdevice, and wherein the method further comprises: outputting to theoutput device an output comprising at least one of: a volume of fluiddispensed from the container, a volume of fluid introduced into thecontainer, a volume of fluid currently available in the container, and avolume of fluid delivered to a particular patient.
 17. A method asrecited in claim 15, wherein a device that is disposed at the openingenables the fluid and the gas to flow through the opening at the sametime.
 18. A method as recited in claim 16, wherein the output deviceincludes at least one of a display, a speaker, and another device, suchthat the act of outputting includes at least one of displaying,broadcasting and transmitting the output.
 19. A computer program productfor use in a system that includes a non-collapsible container, a sensorand a calculating system, wherein the sensor is externally located fromthe container and in fluid communication with the container, such that aflow of a fluid through the container creates hydrostatic pressure atthe sensor, the computer program product including computer-executableinstructions for implementing a method for measuring a flow of a fluidthrough the container, the method comprising: causing a fluid to flowthrough an opening in the container, thereby creating hydrostaticpressure between the container and the externally located sensor, andsuch that a gas is caused to flow through the sensor in response to thehydrostatic pressure; measuring, with the sensor, the amount of gasflowing through the sensor in response to the hydrostatic pressure; andcalculating, with the calculating system, an amount of fluid that hasflowed through the opening in the container based at least in part onthe measured amount of gas flowing through the sensor, wherein a devicethat is disposed at the opening enables the fluid and the gas to flowthrough the opening at the same time, wherein calculating the amount offluid that has flowed through the opening in the container includes:dividing the mass flow of the gas by the density value of the gas toobtain a volume flow of the gas; and integrating, with respect to time,the mass flow of the gas to calculate the volume of gas that has flowedthrough the opening in the container, wherein the volume of gascorresponds directly to a volume of fluid that has flowed through theopening in the container.
 20. A computer program product as recited inclaim 19, wherein causing a fluid to flow through an opening in thecontainer comprises one of dispensing the fluid from the container andintroducing the fluid into the container.
 21. A computer program productas recited in claim 19, wherein the method further includes filteringimpurities from the gas flowing through the sensor.
 22. A computerprogram product as recited in claim 19, wherein the gas flows into thecontainer as it flows through the sensor.
 23. A computer program productas recited in claim 19, wherein measuring the amount of gas flowingthrough the sensor includes: measuring a mass flow of the gas at thesensor; and identifying a density value of the gas.
 24. A computerprogram product as recited in claim 19, wherein the calculating systemis connected with an output device, and wherein the method furthercomprises: outputting to the output device an output comprising at leastone of: a volume of fluid dispensed from the container, a volume offluid introduced into the container, a volume of fluid currentlyavailable in the container, and a volume of fluid delivered to aparticular patient.
 25. A computer program product as recited in claim23, wherein identifying a density value includes at least one ofmeasuring the density value with a density sensor and receiving userinput at the system comprising a predetermined density value.
 26. Acomputer program product as recited in claim 24, wherein the outputdevice includes at least one of a display, a speaker, and anotherdevice, such that outputting includes at least one of displaying,broadcasting and transmitting the output.